1,721,006 research outputs found
In-situ formation of co particles encapsulated by graphene layers
No full textThe process of encapsulating cobalt nanoparticles using a graphene layer is mainly direct pyrolysis. The encapsulation structure of hybrids prepared in this way improves the catalyst stability, which greatly reduces the leaching of non-metals and prevents metal nanoparticles from growing beyond a certain size. In this study, cobalt particles surrounded by graphene layers were formed by increasing the temperature in a transmission electron microscope, and they were analyzed using scanning transmission electron microscopy (STEM). Synthesized cobalt hydroxide nanosheets were used to obtain cobalt particles using an in-situ heating holder inside a TEM column. The cobalt nanoparticles are surrounded by layers of graphene, and the number of layers increases as the temperature increases. The interlayer spacing of the graphene layers was also investigated using atomic imaging. The success achieved in the encapsulation of metallic nanoparticles in graphene layers paves the way for the design of highly active and reusable heterogeneous catalysts for more challenging molecules
Elucidation of Novel Potassium-Mediated Oxidation and Etching of Two-Dimensional Transition Metal Dichalcogenides
No full text© 2021 American Chemical Society.Preparation of edge-rich two-dimensional (2D) transition metal dichalocogenides (TMDs) has been actively investigated with the aim to improve their electrical and catalytic properties. Here, we elucidate the role of potassium ions in oxidation of TMDs and suggest a consequent novel anisotropic etching mechanism driven by self-running oxide droplets. We discover that potassium-mediated oxidation of MoS2 leads to the formation of K-intercalated hexagonal-phase molybdenum oxides (h-KxMoO3), whereas orthorhombic-phase oxides are formed in the absence of potassium ions. Metastable h-KxMoO3 appears to have decomposed into oxide droplets at higher temperature. Self-running of the oxide droplets leads to layer-by-layer anisotropic etching of MoS2 along the armchair direction. The motion of the droplets appears to be triggered by the surface energy instability between the oxide droplets and the underlying MoS2 layer. This study opens new possibilities to design and manufacture novel edge-rich 2D TMDs that do not follow the equilibrium Wulff shape by modulating their oxidation with the assistance of alkali metals and also offers fundamental insights into the interactions between nanodroplets and 2D materials toward edge engineering.11Nsciescopu
Thermally driven phase transition of cobalt hydroxide sheets via cobalt oxides to cobalt nanoparticles
No full textTransition metal oxides, which include many stoichiometric variations, are formed into various crystal structures by the atomic arrangement of cations and anions according to stoichiometric composition and are used for a wide range of applications based on this. Among them, cobalt oxide, which has wide crystal structures depending on the lattice points of the anion and the valence of the Co cation, from its hydroxide formula, is attracting a lot of attention due to its interesting catalytic properties due to its crystal structure. In this study, using the synthesized Co(OH)(2) nanosheets, the real-time behavior of the phase transition that occurs when continuous heat is applied to the sample has been systematically analyzed using an aberration-corrected scanning transmission electron microscope. The layered Co(OH)(2) phase passes through hexagonal CoO and cubic CoO phases to finally become Co nanoparticles, but when the temperature is dropped in the hexagonal phase, spinel Co3O4 is formed. These results suggest that various phases included in transition metal oxides can be selectively implemented according to temperature range control
Interface rich CuO/Al2CuO4 surface for selective ethylene production from electrochemical CO2 conversion
No full textThe electrochemical reduction of carbon dioxide (CO2) to multicarbon hydrocarbons or oxygenate compounds beyond carbon monoxide is of great importance, as it offers a promising way to obtain a renewable fuel of high energy density and dose the carbon cycle. Copper has been considered the predominant and effective electrocatalyst for the CO2 reduction reaction (CO2RR), especially when aiming for ethylene products. However, the selectivity or current density of most catalysts for ethylene production is not satisfactory at competitive prices. Here, we present a newly designed electrocatalyst comprising Al2CuO4 nanosheets uniformly covered with CuO nanoparticles (CuAl-1: CuO/Al2CuO4-23) by phase and interphase engineering, achieving an ultrahigh selectivity of 82.4% for ethylene in an H-cell system with good catalytic stability and material durability for 100 h. In a flow-cell electrolyzer, this catalyst achieves a remarkably high ethylene partial current density of 421 mA cm(-2), substantially higher than the as-synthesized bare CuO (261 mA cm(-2)) counterpart. The results of time-resolved attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) suggest that compared to the CuO catalyst, CuAl-1 enabled high surface coverages of *CO intermediates and strengthened adsorption of *CO for C-C coupling toward *OCCO, which is an intermediate for the production of ethylene. X-ray absorption analysis confirms that Cu oxide species in CuAl-1 are well retained during CO2 reduction, whereas the bare CuO catalyst is completely reduced to the metallic Cu state. Density functional theory calculations propose that a synergistic effect between CuO and Al2CuO4 in the CuAl-1 steers the CO2RR pathway towards ethylene
Air-stable van der Waals PtTe(2) conductors with high current-carrying capacity and strong spin-orbit interaction
Full text linkHigh-performance van der Waals (vdW) integrated electronics and spintronics require reliable current-carrying capacity. However, it is challenging to achieve high current density and air-stable performance using vdW metals owing to the fast electrical breakdown triggered by defects or oxidation. Here, we report that spin-orbit interacted synthetic PtTe(2) layers exhibit significant electrical reliability and robustness in ambient air. The 4-nm-thick PtTe(2) synthesized at a low temperature (∼400°C) shows intrinsic metallic transport behavior and a weak antilocalization effect attributed to the strong spin-orbit scattering. Remarkably, PtTe(2) sustains a high current density approaching ≈31.5 MA cm(−2), which is the highest value among electrical interconnect candidates under oxygen exposure. Electrical failure is caused by the Joule heating of PtTe(2) rather than defect-induced electromigration, which was achievable by the native TeO(x) passivation. The high-quality growth of PtTe(2) and the investigation of its transport behaviors lay out essential foundations for the development of emerging vdW spin-orbitronics
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Atomic transistors based on seamless lateral metal-semiconductor junctions with a sub-1-nm transfer length
Full text linkThe edge-to-edge connected metal-semiconductor junction (MSJ) for two-dimensional (2D) transistors has the potential to reduce the contact length while improving the performance of the devices. However, typical 2D materials are thermally and chemically unstable, which impedes the reproducible achievement of high-quality edge contacts. Here we present a scalable synthetic strategy to fabricate low-resistance edge contacts to atomic transistors using a thermally stable 2D metal, PtTe(2). The use of PtTe(2) as an epitaxial template enables the lateral growth of monolayer MoS(2) to achieve a PtTe(2)-MoS(2) MSJ with the thinnest possible, seamless atomic interface. The synthesized lateral heterojunction enables the reduced dimensions of Schottky barriers and enhanced carrier injection compared to counterparts composed of a vertical 3D metal contact. Furthermore, facile position-selected growth of PtTe(2)-MoS(2) MSJ arrays using conventional lithography can facilitate the design of device layouts with high processability, while providing low contact resistivity and ultrashort transfer length on wafer scales
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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